Thursday, April 10, 2014

Crop rotation is the easiest yield you can get. I call it "the gift that keeps on giving." Corn yield increases 10 to 19% when rotated with soybean, while soybean yield increases 14 to 23% when rotated with corn. For a summary of these rotation responses click here and here. This rotation effect is even more dramatic in stressful years.

The rotation effect lasts at most two years and depends upon the length of the break between similar crops. When you have two or more break years, then the yield of second-year corn is 7 to 8% greater than continuous corn. If there is only one break year, then the yield of second-year corn is the same as continuous corn.

Tillage used to be about controlling weeds and preparing a seedbed. Today it is all about stand establishment. We have many excellent herbicides and advanced technology on our planters. So tillage is often not necessary in today’s corn production systems, except in continuous corn. Tillage responses are more often measured in the northern corn belt and can increase yield 5 to 7%.

How does crop rotation and tillage interact to affect grain yield?

A corn-soybean rotation X tillage study was begun in 1983 at Arlington, WI. The rotation treatments consist of continuous corn, continuous soybean, alternating corn and soybean, and five years of corn followed by five years of soybean. Every phase of these 14 rotation treatments is grown every year. Two tillage treatments designated no-till (NT) and conventional-till (CT) have been practiced. since 1987. No-till consists of one-pass with a 13-wave coulter, followed by trash whippers and then double disc seed openers. Conventional-till is fall chisel plow followed by two spring field-cultivator operations. The continuous corn and soybean plots have been in place 30 years. The results for the previous 20 years (1993-2012) are shown in Figure 1 for corn and Figure 2 for soybean.

Little corn yield differences are observed in rotated corn (CS) and first-year (1C) corn following 5-years of soybean (Figure 1). During the second-year of corn plots that had conventional tillage increased yield 5% over no-till plots (2C). Yield was 10 to 11% greater for conventional-till plots than for no-till plots as the number of continuous corn production years increased (3C, 4C, and 5C). So, tillage is not needed when corn is annually rotated with soybean. Tillage can make up some of the rotation effect over time in continuous corn, but it does not bring yield back to rotated corn yield levels.

Figure 1. Corn yield response to rotation and tillage following five years of soybean during 1993 to 2012 at Arlington, WI. Asterisks indicate statistical differences at P < 0.05. NS= non significant. Percentage values indicate relative differences between tillage systems for a phase in the rotation sequence.

The story is somewhat different for soybean. Grain yield is 3 to 5% greater in no-till than conventional till for the rotated soybean (SC), first- (1S) and second-year (2S) soybean following five years of corn (Figure 2). There is no tillage effect as the number of years of continuous soybean production increases (3S, 4S and 5S) Conventional-till does increase yield over no-till in soybean plots that have been in continuous production for 30 years (SS). So, tillage is not needed when soybean is annually rotated with corn.

Figure 2. Soybean yield response to rotation and tillage following five years of corn during 1993 to 2012 at Arlington, WI. Asterisks indicate statistical differences at P < 0.05. NS= non significant. Percentage values indicate relative differences between tillage systems for a phase in the rotation sequence.

Thursday, April 3, 2014

While reading the Nation Corn Growers Association Yield Contest results, I was struck by the plant populations at planting and harvest. The average planting population of all entrants in the contest was 33,616 plants/A, while state winners averaged 34,821 plants/A, and national winners averaged 39,166 plants/A. The average harvest population for all entrants was 32,160 plants/A, while state winners averaged 33,833 plants/A, and national winners averaged 39,222 plants/A. If we assume that the initial plant population was the planter setting that reflects the number of seeds dropped, then seed survival for all entrants was 96%, while for state winners it was 97% survival, and for national winners it was 100% survival.

I was curious about corn seed survival in Wisconsin. We have traditionally figured that 90% of the seed planted survives to produce a harvestable plant. So to establish a field at 30,000 plants/A, you would need to drop seed at 33,333 plants/A.

Corn seed treatments are required in most planting situations. These treatments protect the plant through the first four- to six-weeks of the corn life cycle. In the past the dominant seed treatment was Captan. Since 2005, we have been tracking the use of seed treatments in the UW corn hybrid performance trials and to date we have had 164 different combinations of seed treatments entered. The question that many growers have asked is, "Has corn seed survival improved in modern production systems?"

Since 2008, the UW hybrid evaluation program has used a precision planter to establish plots. The seeding rate for every plot planted in this program is 34,100 plants/A. At harvest we count the number of plants that survived in 10% of the plots. Various seed treatment combinations are used on hybrids, however, no chemical seed treatments are used in the organic trials.

Where seed treatments are used, corn seed survival averaged 91-92% and was similar in the Early, Late and Specialty trials (Table 1). The organic trials where no seed treatments are used had 82% seed survival. The most challenging location in the program with the lowest seed survival was Seymour where survival was 84%. Other locations that had lower seed survival included Coleman, Lancaster and Marshfield. These sites ranged from 86 to 87% survival. The location with the highest seed survival was Fond du Lac at 95%.

Another study where we routinely measure seed survival is a planting date experiment at Arlington (Table 2). In this study a known quantity of seed is planted and then emerged plants are counted at V5-V6. The optimum time to seed corn at this farm is May 1. Yet, seeding around May 1 does not always result in the best corn seed survival. For example, during 2010 seed survival was 85% in early May with dates before and after where survival was 95% or greater. In most years planting during April decreased seed survival. So to achieve a target harvested population, seeding rate adjustments would need to be made and changed as the planting season progressed.

Corn seed survival likely varies by field. The more challenging fields in our program are in northern Wisconsin. One exception is Lancaster where aggressive tillage is used to prepare the seedbed with soil crusting resulting in some years. Average corn seed survival seems higher than the 90% level we have traditionally used. We should probably be using 92 to 95% seed survival. However, there are numerous exceptions due to seed quality, planting date, tillage system, seed treatment and hybrid.